1. Field of the Invention
The present invention is directed generally to a shaving cutter for shaving or finishing gears, which cutter is provided with a multiplicity of serrations extending on the cutter tooth flanks and including ribs made up by the serrations of the cutter, and the ribs forming the cutter tooth flanks.
The present invention relates more particularly to a shaving cutter suitable for a plunge cut shaving method.
2. Description of the Prior Art
A plunge cut shaving processing method which is commonly employed involves the following steps. As illustrated in FIGS. 3 and 12b, a work gear axis (B--B) and a shaving cutter axis (A--A) are set up at a deliberately calculated cross axis angle. Then the teeth 3, 13 of the shaving cutter 1, 11 are urged with a force and mechanically intruded between the teeth 3a of a work gear 2 in such a direction as to shorten an inter-axis distance (l) between both axes (A--A), (B--B). Meanwhile, lateral sliding caused by contact pressure of the amount Vs shown in FIG. 12b is forced to take place between both teeth due to rotating of the shaving cutter with intermeshing the work gear without imparting an axial feed to both of them. Note that the symbol Vc represents a rotational speed vector of the shaving currer1, 11 at the contact point on the cutter tooth flank in the peripheral direction, Vg denotes a rotational speed vector of a work gear and the amount Vs designates a lateral sliding speed vector along the tooth trace produced due to a difference between vectors Vc and Vg.
In a prior art shaving cutter, a multiplicity of serrations 14 are, as depicted in FIG. 12a, formed on respective tooth flanks formed by the ribs 17a and 17b of the shaving cutter 11 in order to obtain cutting action by utilizing the lateral sliding force, thus providing a multiplicity of serrated cutting edges 15 of ribs.
Generally, a cutter axis intersects a work gear axis (B--B) to be shaved at an angle of approximately 4.degree..about.15.degree. which are varied by gear element, whereby the great majority of cutters have their teeth each assuming a helical gear configuration (i.e. each tooth has a helix angle).
Hence, in a prior art shaving cutter as shown in FIG. 12c, the cutter is provided with ribs 27a, 27b, of the serration 24a, 24b orthogonal to a cutter axis (A--A), called axial serrations. These serrations 24a, 24b are manufactured by employing a combshaped cutting tool 26a.
In another prior art shaving cutter illustrated in FIG. 12d, there are provided ribs 17a, 17b of the serrations 14a, 14b orthogonal to the centerline of each of the tooth flanks (C--C), called normal serrations. These serrations 14a, 14b are also manufactured by use of a comb-shaped cutting tool 16b.
However, as illustrate in FIG. 12c, rake angles or hook angles .alpha.a and .alpha.b at cutting edges 25a, 25b of the cutter 21 having the axial serrations 24a, 24b, are completely reverse in positive and negative, with respect to upper and lower tooth flanks as viewed in FIG. 12c formed by the ribs 27a, 27b of the serration, so that the surface finish on both tooth flanks of the shaved gear becomes nonuniform.
On the contrary, in the other prior art cutter having the normal serrations 14a, 14b as seen in FIG. 12d, since both rake angles or hook angles (FIG. 12c, .alpha.a, .alpha.b) are perpendicular to the tooth flank center line (C--C), the surface finish effected by this cutter on both sides of the tooth flanks of the work gear become more symmetric. Thus, actual cutting amounts, as well as surface roughness on both side of the worked gear flanks are symmetrical, on one hand, however, on the other hand, it is known that the absolute cutting quality or sharpness is considerably deteriorated. More specifically, apropos of the shaving work, since the depth of a cut (0.002.about. 0.010 mm) per one gear rotation is remarkably less compared with general machining, a high bite property of the cutting edge is required. For this reason, a shaving cutter having a positive rake or hook angle has more advantages. Whereas in the above normal serration cutter, the rake angle is zero. This implies that the rake angle does not contribute to the cutting quality. As a result, the above normal serration cutter, though it is one of the finishing tools, does not always achieve a desirable result, because the tooth profile and the deflection or runout of the tooth grooves of shaved gear tends to follow the accuracy of the pre-shaving finish (processing).